Electromagnetic locks for securing doors or gates are well known in the prior art. In a typical installation, a magnetically-susceptible plate is mounted on a door, and an electromagnet is mounted on a door jamb or gate post. When the electromagnet is energized, is in contact with the plate, and the door is closed, the plate becomes an armature for the electromagnet. Magnetic flux passes between the electromagnet and the armature, attracting the armature to the electromagnet and thus providing a mechanism for locking the door to the jamb. When the magnetic loop is complete, by contact of the armature with the electromagnet, the magnetic flux density is at a maximum. If the armature is separated from the electromagnet, the magnetic flux is decreased as a function of the distance therebetween. Thus, a device that can sense the strength of the magnetic field can be configured as an alarm mechanism for a door that is not fully or properly secured by an electromagnetic lock or for a door that is being forced open by an attempt to forcibly separate the armature and electromagnet.
It is well known in the prior art to employ a lock security alarm system based upon the Hall Effect, wherein the voltage potential orthogonal to a magnetic field is proportional to the strength of the magnetic field. Prior art devices typically employ a single Hall Effect device.
A significant problem with such a prior art system is that only the magnetic field immediately adjacent the Hall Effect device is actually monitored. Thus, an armature plate may be offset laterally by up to several inches from the electromagnet, thus significantly reducing the total holding force of the lock but still having the same magnetic strength near the Hall Effect device. Furthermore, use of a single Hall Effect device may lead to monitoring only half of the actual magnetic field available, as there are two overlapping magnetic fields in operation with a typical E-shaped magnetic core used in many prior art electromagnetic locks.
What is needed in the art is an improved Hall Effect lock security system that assures correct three-dimensional alignment and contact of an electromagnet lock and armature.
It is a principal object of the present invention to improve the reliability of electromagnetic locking of a door to a jamb.